I'm a artist working on a series of small concrete models of buildings, probably 100cm square at their largest. I'm looking for advice on making moulds, should i just invert the building? Or any other materials that would acheive the same look as concrete.
I realized that I totally ignored the second part of your question. Molds are dependent on what exactly you're making. If you're making a solid block and only have to demold the exterior then yeah just invert the building, look into cast making for other cast products for some best practices. My advice is to plan your pour and plan your demold. With rockite, if you mix it well, you can do two pours and have a cold joint so if you're pouring multiple floors you can break it up. Line the interior of your molds with Tyvek tape. It is thin and rockite won't stick to it so you can just pop your molds off. Finally, vibrate your pour just like concrete but don't overdo it, just like concrete. It is a fast acting cement so make sure you're ready to rock when you start mixing it. It generates a bit of heat as it cures and if you mix it a little wet (for fluidity) then it will fully cure in 20ish minutes. I experimented a lot with concrete, rockite, and plaster in school. The reason I like rockite better than plaster is that I can invest my time in getting the mold right rather than having to bake in additional time for curing.
Look at using plaster of paris that you tint the mix or surface paint afterward to a concrete color. I've seen some nice scale models made with Rockite, but also some epic fails where people had a lot of problems with pouring it into small molds. There were also issues with the Rockite hardening in the bucket before the whole mold could be filled.
Rockite is a grout and not really concrete, so the notion of modeling a concrete building in Rockite "real concrete" is just architecture school silliness.
I see a guy on insta all the time doing these models or little sculptures, molds made of dense foam, can't find it right now.
Dec 3, 24 2:51 pm ·
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OddArchitect
Is he using XPS and a hot knife?
Dec 3, 24 2:57 pm ·
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JLC-1
I don't know, looks more stiff than xps
Dec 4, 24 11:59 am ·
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OddArchitect
Do you know if the artist was carving it with hand tools or are they using a hot knife / blade?
Dec 4, 24 12:44 pm ·
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JLC-1
doesn't show the making of the mold, just the form removal.
Dec 4, 24 1:14 pm ·
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OddArchitect
Interesting. I must look for that video. Thanks for mentioning it!
Dec 4, 24 6:23 pm ·
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oli_miles
Have you find it, id like to check that out too?
Dec 4, 24 9:16 pm ·
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JLC-1
couldn't find the guy I was talking about, but this guy does something similar, with a combination of materials for the mould
https://www.instagram.com/david_umemoto/
good catch on noting the proposed size... To accomplish this in the real material, OP would have to use actual concrete with internal reinforcement. It's not really small, it's going to be like pouring a section of sidewalk.
That is more what I'm leaning towards to get that look as it is closer to what i have expierience in but it might still be interesting to try concrete.
Might need some clarification from the OP. In my experience, 100 cm square would indicate 100 cm x 100 cm, but 100 square cm would indicate 10 cm x 10 cm.
Dec 4, 24 7:33 pm ·
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oli_miles
There's been some confusion about that. I mean that each side would be 10cm or thereabouts.
My profile picture is one of about 20+ concrete models of a similar scale that I've made both as a student and as a professional. Here's my two cents:
- I've had my best results with fast-curing concrete. Pros:it includes very little aggregate since it's usually used for small garden jobs, so it will usually get into all nooks and crannies of the mold. Cons: You need to pour and vibrate it very quickly as it sets within minutes. Cement will do as well, but it's stickier and harder to pour at times. Visually it'll do the trick. Rockite works well and it's excellent to pour, as its viscosity seems to increase right after you pour it. It's brittle though.
- As for molds: If you wanna go low-tech, use foam. easy to cut, you can dissolve the mold away with acetone. it will require cleanup afterwards though, with a toothbrush. Some of the foam will turn into solid-ish bits and cling to the concrete surface. If you use wood, make sure it is 100% watertight. Otherwise the wood will absorb the water from the concrete and your model will crumble. If you wanna go mid to high tech, laser cut acrylic is a wonderful material. It's naturally non-stick, and if you use the clear type you can see if your concrete has reached all corners. 3d printed parts work well but the texture of the printing layers will give it some tooth so concrete might stick. Treat it with mold release, whether commercial or homemade.
- Mold release: again, if you wanna go very low tech, some dish soap diluted in water and sprayed shortly before pouring will work. If you wana go a bit more complex but without going commercial, vaseline emulsified in mineral spirit will be easy to apply, and when the spirit evaporates it'll leave a thin but consistent layer of vaseline on the mold which will work well as a release.
I hope this all helps, happy to answer any other questions if needed.
That sounds like a really cool project! For making molds for your concrete models, inverting the building is a common method and can work well, especially if you're looking for clean lines. You can use a variety of materials for the molds, such as silicone, which is flexible and allows for easy release of the concrete once it sets.
Another option is to use a hard material like plywood or MDF, but you’ll need to coat it with a release agent (like petroleum jelly or cooking spray) to help get the concrete out smoothly.
If you're open to alternatives to concrete, you might consider materials like resin or plaster. Both can give you a similar finish and might be lighter and easier to work with depending on the size.
Good luck with your models! Can’t wait to see the final results!
Dec 10, 24 6:57 am ·
·
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Small scale concrete models.
I'm a artist working on a series of small concrete models of buildings, probably 100cm square at their largest. I'm looking for advice on making moulds, should i just invert the building? Or any other materials that would acheive the same look as concrete.
Thanks in advance.
Rockite is the best product imo for modeling concrete. It is expensive but it is rock solid and easy to work with.
I realized that I totally ignored the second part of your question. Molds are dependent on what exactly you're making. If you're making a solid block and only have to demold the exterior then yeah just invert the building, look into cast making for other cast products for some best practices. My advice is to plan your pour and plan your demold. With rockite, if you mix it well, you can do two pours and have a cold joint so if you're pouring multiple floors you can break it up. Line the interior of your molds with Tyvek tape. It is thin and rockite won't stick to it so you can just pop your molds off. Finally, vibrate your pour just like concrete but don't overdo it, just like concrete. It is a fast acting cement so make sure you're ready to rock when you start mixing it. It generates a bit of heat as it cures and if you mix it a little wet (for fluidity) then it will fully cure in 20ish minutes. I experimented a lot with concrete, rockite, and plaster in school. The reason I like rockite better than plaster is that I can invest my time in getting the mold right rather than having to bake in additional time for curing.
Thanks for the in depth response thats super helpful!
Look at using plaster of paris that you tint the mix or surface paint afterward to a concrete color. I've seen some nice scale models made with Rockite, but also some epic fails where people had a lot of problems with pouring it into small molds. There were also issues with the Rockite hardening in the bucket before the whole mold could be filled.
Rockite is a grout and not really concrete, so the notion of modeling a concrete building in Rockite "real concrete" is just architecture school silliness.
I see a guy on insta all the time doing these models or little sculptures, molds made of dense foam, can't find it right now.
Is he using XPS and a hot knife?
I don't know, looks more stiff than xps
Do you know if the artist was carving it with hand tools or are they using a hot knife / blade?
doesn't show the making of the mold, just the form removal.
Interesting. I must look for that video. Thanks for mentioning it!
Have you find it, id like to check that out too?
couldn't find the guy I was talking about, but this guy does something similar, with a combination of materials for the mould https://www.instagram.com/david_umemoto/
Thanks JCL-1!
https://www.instagram.com/borisipsum?igsh=MXByMWs2ZHY1bGVwZw==
Found it
100 cm sq in concrete? Height?
That's a massively heavy model.
Need more information to advise in any intelligent way
good catch on noting the proposed size... To accomplish this in the real material, OP would have to use actual concrete with internal reinforcement. It's not really small, it's going to be like pouring a section of sidewalk.
100 cm sq is 10 cm a side, ~4". not that big
I may very well be wrong but I read it as 100cm per side
Make it out of foam and then skim coat and spray paint it to look like concrete. Much more efficient, lighter weight, and easier to do.
I mean yeah, but then it's not concrete. We all know concrete is the best.
If you make it out of foam, then how will we be able to throw it through the window it's modeled after?
Having a model weigh 800 lbs is .... really something.
If you're strong enough you can still throw the concrete model out the window. ;)
That is more what I'm leaning towards to get that look as it is closer to what i have expierience in but it might still be interesting to try concrete.
Might need some clarification from the OP. In my experience, 100 cm square would indicate 100 cm x 100 cm, but 100 square cm would indicate 10 cm x 10 cm.
There's been some confusion about that. I mean that each side would be 10cm or thereabouts.
Hi there,
My profile picture is one of about 20+ concrete models of a similar scale that I've made both as a student and as a professional. Here's my two cents:
- I've had my best results with fast-curing concrete. Pros:it includes very little aggregate since it's usually used for small garden jobs, so it will usually get into all nooks and crannies of the mold. Cons: You need to pour and vibrate it very quickly as it sets within minutes. Cement will do as well, but it's stickier and harder to pour at times. Visually it'll do the trick. Rockite works well and it's excellent to pour, as its viscosity seems to increase right after you pour it. It's brittle though.
- As for molds: If you wanna go low-tech, use foam. easy to cut, you can dissolve the mold away with acetone. it will require cleanup afterwards though, with a toothbrush. Some of the foam will turn into solid-ish bits and cling to the concrete surface. If you use wood, make sure it is 100% watertight. Otherwise the wood will absorb the water from the concrete and your model will crumble. If you wanna go mid to high tech, laser cut acrylic is a wonderful material. It's naturally non-stick, and if you use the clear type you can see if your concrete has reached all corners. 3d printed parts work well but the texture of the printing layers will give it some tooth so concrete might stick. Treat it with mold release, whether commercial or homemade.
- Mold release: again, if you wanna go very low tech, some dish soap diluted in water and sprayed shortly before pouring will work. If you wana go a bit more complex but without going commercial, vaseline emulsified in mineral spirit will be easy to apply, and when the spirit evaporates it'll leave a thin but consistent layer of vaseline on the mold which will work well as a release.
I hope this all helps, happy to answer any other questions if needed.
That sounds like a really cool project! For making molds for your concrete models, inverting the building is a common method and can work well, especially if you're looking for clean lines. You can use a variety of materials for the molds, such as silicone, which is flexible and allows for easy release of the concrete once it sets.
Another option is to use a hard material like plywood or MDF, but you’ll need to coat it with a release agent (like petroleum jelly or cooking spray) to help get the concrete out smoothly.
If you're open to alternatives to concrete, you might consider materials like resin or plaster. Both can give you a similar finish and might be lighter and easier to work with depending on the size.
Good luck with your models! Can’t wait to see the final results!
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